3 years ago

[ASAP] Validation of pH Standards and Estimation of the Activity Coefficients of Hydrogen and Chloride Ions in an Ionic Liquid, Ethylammonium Nitrate

[ASAP] Validation of pH Standards and Estimation of the Activity Coefficients of Hydrogen and Chloride Ions in an Ionic Liquid, Ethylammonium Nitrate
Ryo Kanzaki, Hikaru Daiba, Hitoshi Kodamatani, Takashi Tomiyasu
We selected and validated the pH values of three standard materials that function in the protic ionic liquid, ethylammonium nitrate (EAN). The pH values of 0.05 mol kg–1 phthalate, oxalate, and phosphate buffers were 4.93 (0.04), 2.12 (0.04), and 7.13 (0.06), respectively (the values in the parentheses denote the standard deviation). Because the pH of EAN ranges from 0 to 10, with a neutral pH of 5, these materials are usable as acidic, basic, or neutral standards. The standard electrode potential of silver–silver chloride in EAN was 127.2 (1.7) mV. The activity coefficients of hydrogen and chloride ions remain equal to unity in EAN of a wide concentration range, which indicates that the effective ionic strength is independent of the solute ion concentration. In addition, the estimated value of the transfer activity coefficient of chloride ion suggests a weaker solvation in EAN compared with water in spite of a ubiquitous cation (C2H5NH3+). These behaviors of ions in EAN can be explained by the unique solvation in the ionic liquid through direct ion–ion electrostatic interactions.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcb.8b08870

DOI: 10.1021/acs.jpcb.8b08870

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